(1) Field of the Invention
The present invention relates to an aqueous coating composition for golf ball, capable of forming a coating film of high durability superior in impact resistance, abrasion resistance, contamination resistance, etc., as well as to a golf ball coated with the coating composition.
(2) Description of Related Art
Two-pack type urethane resin coatings are in wide use for various reasons such as (a) they can form a cured film even at ordinary temperatures, (b) the urethane linkage formed thereby is chemically stable and has high water resistance, chemical resistance, etc., and (c) the polyol and polyisocyanate used as the raw materials can be selected widely and the designing of a coating having desired physical and chemical properties can be made at a high freedom. Conventional urethane resin coatings, however, use a large amount of a volatile organic solvent and this has various problems such as handling of hazardous substance, air pollution, offensive odor, waste disposal, aggravation of coating environment, and the like. A recent movement for protection of global environment has accelerated the development of powder coating, ultraviolet-curing coating and aqueous coating. European countries and U.S.A are advanced in the development of coatings of hazard-free and resource saving type, and aqueous coatings are a main stream. Specific forms of aqueous coatings are aqueous solution, emulsion and colloidal dispersion. In the aqueous solution (of resin), the resin used is allowed to have a functional group for hydrophilicity; a curing agent is used except for when the resin is a particular alkyd resin; and heating and drying at high temperatures is necessary. In the emulsion and colloidal dispersion, hydrophobic polymer particles have, on the surfaces, an ion, a hydrophilic polymer, a low-molecular emulsifier, etc. adsorbed or absorbed; and the coating film formed has excellent water resistance and durability. These aqueous coatings, as compared with organic solvent type coatings, are inferior in film properties and have problems in application to a golf ball which requires impact resistance, abrasion resistance and contamination resistance. There is a description on an aqueous two-pack type polyurethane coating for golf ball, in U.S. Pat. No. 5,830,938. In this coating, however, the hydroxyl value determined from the hydroxyl equivalent of the polyol used is as low as 37 to 14, which does not satisfy the impact resistance, abrasion resistance, contamination resistance, etc. intended by the present invention.
In order for a coating to be able to form a coating film satisfactory in impact resistance, abrasion resistance, contamination resistance, etc., the coating film formed must be tough. In order to achieve it, the materials used in the coating need to have structural hardnesses and a crosslinked structure must be formed between polymer molecules. Urethane resins are most appropriate in the availability of the raw materials, the controllability of their reaction, and the achievability of required properties. Hence, it has been desired to develop, from an aqueous urethane resin, a coating for golf ball, capable of forming a film equivalent to that formed by solvent type urethane coatings.
The present inventors made a study in order to alleviate the above problems. As a result, the present invention has been completed. The present invention lies in the following (1) to (10).
(1) An aqueous coating composition for golf ball, comprising:
a water-soluble urethane polyol having a hydroxyl value of 100 to 300 mgKOH/g, obtained by reacting a polyol component and a polyisocyanate component, and
a hydrophilic group-containing polyisocyanate.
(2) An aqueous coating composition for golf ball, comprising:
a water-soluble urethane polyol having a hydroxyl value of 100 to 300 mgKOH/g, obtained by reacting a polyol component and a polyisocyanate component,
a water-dispersible urethane resin, and
a hydrophilic group-containing polyisocyanate.
(3) An aqueous coating composition for golf ball, comprising:
a water-soluble urethane polyol having a hydroxyl value of 100 to 300 mgKOH/g, obtained by reacting a polyol component and a polyisocyanate component,
a water-dispersible acrylic resin, and
a hydrophilic group-containing polyisocyanate.
(4) The aqueous coating composition for golf ball according to any of the above (1) to (3), wherein at least part of the polyol component is a polyol having an alicyclic structure.
(5) The aqueous coating composition for golf ball according to any of the above (1) to (3), wherein at least part of the polyol component is a polyester polyol obtained by reacting a polybasic acid having an alicyclic structure, with a polyol.
(6) The aqueous coating composition for golf ball according to any of the above (1) to (3), wherein at least part of the polyol component is a polyester polyol obtained by reacting a polyol having an alicyclic structure, with a polybasic acid.
(7) The aqueous coating composition for golf ball according to the above (1), wherein at least part of the polyol component is a polyester polyol obtained by reacting a polyol having an alicyclic structure, with a polybasic acid having an alicyclic structure.
(8) The aqueous coating composition for golf ball according to the above (3), wherein at least part of the water-dispersible acrylic resin is a water-dispersible acrylic resin having an isocyanurate ring.
(9) The aqueous coating composition for golf ball according to any of the above (1) to (3), wherein the hydrophilic group-containing polyisocyanate is a hydrophilic group-containing polyisocyanate having an isocyanurate ring.
(10) A golf ball obtained by coating a golf ball body with the aqueous coating composition set forth in any of the above (1) to (3).
The water-soluble urethane polyol used in the present invention is a compound having a hydroxyl value of 100 to 300 mgKOH/g, obtained by subjecting a polyol component and a polyisocyanate component to urethanization. The hydroxyl value range of 100 to 300 mgKOH/g possessed by the water-soluble urethane polyol can promise a coating film having intended property levels in impact resistance, abrasion resistance, contamination resistance, etc.
The polyol component is a polyol having, in the molecule, groups necessary for obtaining sufficient water solubility, or a mixed polyol of the above polyol and other polyol. The mixed polyol is preferred because it makes easy the designing of a water-soluble urethane polyol having required properties.
Preferably, at least part of the polyol component, specifically 5 to 60% of the total polyols (including the raw materials for synthesis of polyester polyol, etc.) is a polyol having an alicyclic structure. Also preferably, at least part of the polyol component is a polyester polyol obtained by reacting a polybasic acid containing 10 to 70% of a polybasic acid having an alicyclic structure, with a polyol. Also, the polyol component may be a polyester polyol obtained by reacting a polyol partially containing a polyol having an alicyclic structure, with a polybasic acid, or a polyester polyol obtained by reacting a polyol partially containing a polyol having an alicyclic structure, with a polybasic acid partially containing a polybasic acid having an alicyclic structure.
As the polyol having, in the molecule, groups necessary for obtaining sufficient water solubility, there is preferred a diol having carboxyl group in the molecule, for reasons of raw materials availability, etc. Specifically, there are mentioned dimethylolpropionic acid, 2,2-dimethylolacetic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxypropionic acid, dihydroxysuccinic acid, etc.
As the polyol other than the polyol having, in the molecule, groups necessary for obtaining sufficient water solubility, there are specifically mentioned, for example, diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, hexylene glycol, dimethylolheptane, polyethylene glycol, polypropylene glycol and the like; triols such as trimethylolethane, trimethylolpropane, glycerine, tris-2-hydroxyethyl isocyanurate and the like; tetraols such as pentaerythritol and the like. As the polyol having an alicyclic structure, there are mentioned 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecanediol, tricyclodecanedimethanol, hydrogenated bisphenol A, etc. The polyol further includes a polyester polyol, an acrylic polyol, etc.
The polyester polyol is obtained by polycondensation of a polyol and a polybasic acid. As this polyol, there are mentioned, for example, the above-mentioned diols, triols, tetraols and polyols having an alicyclic structure. As the polybasic acid, there are mentioned, for example, aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, azelaic acid, dimer acid and the like; aliphatic unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, citraconic acid and the like; aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid and the like; dicarboxylic acids having an alicyclic structure, such as tetrahydrophthalic acid, hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, endomethylenetetrahydrophthalic acid and the like; and tris-2-carboxyethyl isocyanurate.
The acrylic polyol is a (co)polymer of hydroxyl group-containing acrylic monomers. As such acrylic monomers, there are mentioned, for example, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate and hydroxybutyl acrylate.
These polyols can be used singly or in admixture, depending upon the properties required for the coating film formed.
The polyisocyanate component used for urethanization with the polyol component is an ordinarily used polyisocyanate of aromatic type, aliphatic type, alicyclic type or other type. There are specifically mentioned tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,4-cyclohexylene diisocyanate, naphthalene diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, 1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane, etc. These compounds can be used singly or in admixture.
In the urethanization of the polyol component and the polyisocyanate component, there can be used, as necessary, a tin-based compound (e.g. dibutyltin dilaurate) or an amine type compound (e.g. triethylamine) as a reaction catalyst.
As the organic solvent usable as a solvent in the reaction, there are mentioned acetone, methyl ethyl ketone, tetrahydrofuran, dimethylformamide, dioxane, dimethyl sulfoxide, N-methyl-2-pyrrolidone, etc.
As the base used for neutralization, there are mentioned ammonia, methylamine, ethylamine, propylamine, butylamine, ethanolamine, propanolamine, diethanolamine, dimethylamine, diethylamine, triethylamine, N,N-dimethylethanolamine, etc. These bases can be used singly or in admixture, depending upon the stability of the water-soluble urethane polyol obtained. The preferable amount of the base used for neutralization is, for example, 0.6 to 1.3 equivalents per equivalent of the carboxyl group in water-soluble urethane polyol.
The water-soluble urethane polyol can be used in combination with a water-dispersible urethane resin or with a water-dispersible acrylic resin. The proportion of the water-dispersible urethane resin or water-dispersible acrylic resin used in combination with the water-soluble urethane polyol can be any level. Part of the water-dispersible acrylic resin is preferably a copolymer obtained by using an acrylate monomer having an isocyanurate ring. The water-dispersible acrylic resin is used in an amount of preferably 70% or less in terms of solid content, relative to the total amount of the water-soluble urethane polyol and the water-dispersible acrylic resin.
The water-dispersible urethane resin is obtained, for example, by reacting, in an organic solvent, a polyol having two or more hydroxyl groups in the molecule, with a polyol having, in the molecule, groups necessary for obtaining sufficient water solubility, with a polyisocyanate being added dropwise, conducting neutralization with a base, adding deionized water and dropwise adding a chain extender with stirring using a high-speed dispersion mixer, to give rise to a reaction. As the above materials used in production of the water-dispersible urethane resin, i.e. the polyol having two or more hydroxyl groups in the molecule, the polyol having, in the molecule, groups necessary for obtaining sufficient water solubility, the polyisocyanate, the organic solvent, the base used for neutralization, the catalyst, etc., there are mentioned the corresponding materials used in production of the water-soluble urethane polyol. As the chain extender, there are mentioned amine compounds such as ethylenediamine, 1,2-propanediamine, 1,4-tetramethylenediamine, 1,6-hexamethylenediamine, 1,4-cyclohexanediamine, isophoronediamine, 4,4xe2x80x2-cyclohexylmethanediamine, piperazine, hydrazine, diethylenetriamine, triethylenetetramine and the like; polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, polyethylene glycol and the like; water; and so forth.
The water-dispersible acrylic resin is obtained by subjecting an ethylenically unsaturated compound to addition polymerization. As the ethylenically unsaturated compound, there are mentioned, for example, acrylic acid; methacrylic acid; acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, octyl acrylate, decyl acrylate, octadecyl acrylate, 2-hydroxyethyl acrylate and the like; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, amyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, decyl methacrylate, 2-hydroxyethyl methacrylate and the like; aromatic vinyl compounds such as styrene, xcex1-methylstyrene, divinylbenzene and the like; vinyl compounds such as vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride and the like; vinyl cyanide compounds such as acrylonitrile, methacrylonitrile and the like; diolefin compounds such as butadiene, isoprene and the like; amide compounds such as acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N-methylolacrylamide and the like; acrylic acid compounds having an isocyanurate ring, such as isocyanuric acid ethylene oxide-modified diacrylate, isocyanuric acid ethylene oxide-modified triacrylate and the like; and mixtures of two or more kinds of the above.
The hydrophilic group-containing polyisocyanate used for curing the water-soluble urethane polyol or its combination with the water-dispersible urethane resin or the water-dispersible acrylic resin is specifically a hydrophilic compound obtained, for example, by reacting an aromatic, aliphatic or alicyclic polyisocyanate with a polyol such as polyether polyol, polyester polyol or the like. As the aromatic, aliphatic or alicyclic polyisocyanate, there are preferred, for example, hexamethylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane, and their derivatives having biuret linkage, urethane linkage, uretdione group or isocyanurate ring. Of these, most preferred are derivatives having isocyanurate ring. As to the proportions of (1) the water-soluble urethane polyol or its combination with the water-dispersible urethane resin or the water-dispersible acrylic resin and (2) the hydrophilic group-containing polyisocyanate, used in their reaction, the equivalent ratio of the isocyanate groups in the hydrophilic group-containing polyisocyanate, relative to the total hydroxyl groups in the water-soluble urethane polyol or its combination with the water-dispersible urethane resin or the water-dispersible acrylic resin is preferably 0.8 to 3.0 viewed from the impact resistance, abrasion resistance, contamination resistance, etc. required for the golf ball coated with the aqueous coating composition of the present invention.
The aqueous coating composition for golf ball according to the present invention may further contain, as necessary, additives such as pigment, dye, dispersion stabilizer, viscosity-controlling agent, ultraviolet absorber, antioxidant, light stabilizer, fluorescent whitening agent, leveling agent, antifoaming agent, curing catalyst and the like, in order to impart various properties to the composition.
The aqueous coating composition of the present invention has excellent stickiness to, for example, the ionomer resin used as a surface material for golf ball, and can be used not only as a top coat but also as an intermediate coat or an undercoat.
The aqueous coating composition of the present invention can be applied to a golf ball by spray coating, electrostatic coating or the like and can be cured and dried at temperatures of 60xc2x0 C. or lower.